Development of a new dynamometer for measuring grip strength applied on a cylindrical handle.

The objective of this study is to enhance the understanding of the hand grip force applied to a cylindrical handle and to develop a new dynamometer for measuring maximum grip force or grip strength. Specifically, a 40 mm instrumented cylindrical handle with six measuring arms was developed. A theoretical model was proposed and used to analyze the principle of the measurement. Human test subjects were used in conducting two sets of experiments to evaluate the handle and to assess the measurement method. This study confirmed that some friction force exists in the grip-only action, but its level is not comparable with the normal force. This study also found that the friction force can stabilize the grip action and marginally increase the grip strength. No reliable correlation between the grip strengths measured with the 40 mm cylindrical handle and Jamar handle with a 47.6 mm span was observed. This suggests that grip strength measured with Jamar handle may not be reliably applicable to the design and risk assessment of some tools or machines with cylindrical handles. In contrast, the cylindrical handle proved to be able to determine the overall grip strength for a subject, as well as show the grip force distribution around the circumference of the handle. The handle is accurate with less than 4% error, and it demonstrates that the measurement is independent of the loading position along the handle. Therefore, this study concluded that this new dynamometer is suitable for measuring grip strength with sufficient precision.